Basic Oxygen Furnace steel slag and apatite for sustainable - - PowerPoint PPT Presentation

Basic Oxygen Furnace steel slag and apatite for sustainable phosphorus removal at small wastewater treatment plants

SWWS2016

Naiara Fonseca

PhD student 15th September 2016

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Why remove phosphorus and to what extent?

• The largest source of phosphorus (P) in rivers in the UK is sewage effluent
• Current consents based on the Urban Wastewater Treatment Directive
• Water Framework Directive – Good ecological status
• New TP consents 1-2 mg/L, and as low as 0.5 mg/L regardless of WWTP size

Background

WWTP size (population equivalent) Total Phosphorus consent (mg/L) < 10,000 none 10,000 – 100,000 2 > 100,000 1

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Conventional solution: chemical dosing + tertiary filtration

Solutions to remove P at small WWTP

Sand filter Coagulant Coagulant

Screens Primary Settlement Tanks Trickling Filters Humus tanks

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Conventional solution: chemical dosing + tertiary filtration

Solutions to remove P at small WWTP

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Sustainable solution: Constructed wetlands with reactive media

Solutions to remove P at small WWTP

Constructed wetlands with P reactive media

Screens Primary Settlement Tanks Trickling Filters Humus tanks

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Sustainable solution: reactive media within constructed wetlands

Solutions to remove P at small WWTP

BASIC OXYGEN FURNACE STEEL SLAG APATITE

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Sustainable solution: reactive media within constructed wetlands

Solutions to remove P at small WWTP

BASIC OXYGEN FURNACE STEEL SLAG APATITE

Material Origin Type of material Price BOF steel slag Tarmac (Wales) Waste £ Apatite TIMAB (France) Manufactured £££

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Configuration

Full-scale constructed wetland trial

Bed Material Type vHRT (h) Days in operation 1 SS 10‐20mm Horizontal sub‐ surface flow 24 379 2 SS 4‐10mm 24 374 3 SS 2‐6mm 24 291 4 Apatite 2‐8mm 12 404

< 10% of QT TP = 3 - 4 mg/L

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Configuration

Lab-scale column experiments

Column Material vHRT (h) Flow Water type Days in

• peration

1 SS 4‐10mm 6, 24, 48 Downwards, submerged Synthetic,

NH4H2PO4

45 2 Apatite 2‐8mm 60 3 Apatite2 2‐8mm 6

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Results

Full-scale constructed wetland trial

• All slag fractions <0.5 mg/L for most of the time. Apatite consistently <0.5 mg/L
• Apatite higher P removal capacity than slag
• Conditioning period

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Results

Full-scale constructed wetland trial

• High effluent pH linked to Ca(OH)2 dissolution
• Effluent pH decrease with time for both materials, but higher for apatite and <9

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Results – Phosphorus removal

Full-scale constructed wetland trial

• Removal efficiency: apatite > small slag > medium slag > large slag

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Results – Effect of HRT on steel slag performance

Lab-scale column experiments

• Higher P removal for higher HRT
• Higher effluent pH for higher HRT

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Results – Effect of HRT on apatite performance

Lab-scale column experiments

• High P removal regardless of HRT
• Higher effluent pH for higher HRT, but lower than slag

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Results – comparison of two different apatite materials

Lab-scale column experiments

• So far, same P removal for both apatite materials
• Apatite2 lower effluent pH linked to the binder employed (Fe based instead of Ca based)

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Conclusions

• Constructed wetlands with reactive media can be a sustainable and

appropriate solution for P removal at small WWTPs.

• BOF steel slag could be employed for consents > 1.5 mg TP/L.
• Apatite shows higher P removal capacity than BOF steel slag.
• HRT key operational parameter for slag, but less for apatite.
• New apatite generation produces lower effluent pH while

maintaining same high level of P removal.

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Naiara Fonseca

Naiara.FonsecaGalarraga@thameswater.co.uk N.Fonseca@cranfield.ac.uk

THANK YOU FOR YOUR ATTENTION

Basic Oxygen Furnace steel slag and apatite for sustainable phosphorus removal at small wastewater treatment plants